Method of making gray cast iron



Jan. 10, 1950 H. c. GRIGGS ET AL METHOD OF MAKING GRAY CAST IRON Filed May 26, 1948 w i M g 1 m a 1, 411 L. A: f a r, M A.

//1ven7ors: HENRY C. GR/aas LAURENCE J. L/mL/E/v Patented Jan. 10, 1950 UNITED STATES PATENT OFFICE METHOD OF MAKING GRAY CAST IRON Henry C. Griggs and Laurence J. Litalien, Waterbury, Conn., assignors to The Waterbury Farrel Foundry & Machine 00., Waterbury, Conn., a corporation of Connecticut Application May 26, 1948, Serial No. 29,355

3 Claims. 1

This invention relates to the manufacture of cast iron, and more particularly to a method of treating cast iron in the molten state to produce a gray cast iron alloy having increased tensile strength and transverse strength.

One object of this invention is to produce a gray cast iron of the above nature which will possess a greater density, improved machinability, rigidity at high temperatures, and minimum hardness as cast.

A further object is to provide an improved gray cast iron of the above nature which will possess a peak hardness of from 550 to 600 B. H. N. when heat treated, and which will take a high polish.

A further object is to provide a gray cast iron of the above nature which will be cheap to manufacture from scrap cast iron, pig iron, or steel scrap in any desired proportions.

A further object is to provide an improved gray cast iron which has been completely deoxidized, having a decreased number of blowholes and segregations, and in which the pearlite is stabilized.

A further object is to provide a method of producing an improved gray cast iron of the above nature which consists of introducing into a cupola or other container of molten cast iron, an iron capsule containing a small quantity of a material containing fluorine in chemical combination with one or more other elements such as copper or boron and in which the fluorine serves as a. catalyst and is dissipated by volatization before casting the metal.

With these and other objects in view there have been disclosed in the accompanying drawing and specification two examples in which the invention may be conveniently embodied in practice.

In the drawing,

Fig. 1 represents a microphotograph at 1000 diameters after etching in 2% Nital of the gray cast iron produced by the process of the present invention and showing the Pearlite and graphite structure thereof.

Fig. 2 is a microphotograph at 100 diameters without etching, of a sample of common gray cast iron showing the normal type of long large interlacing graphite flakes.

Fig. 3 is a similar microphotograph at 100 diameters, without etching, of a sample of gray cast iron made by the process of the present invention. using a .05% cupric fluoride addition, and showing the short separated graphite flakes.

Example I According to the first example, five pounds of cupric fluoride (CuF22HzO) are placed in an iron capsule and dropped into 2,000 pounds of molten iron in a furnace, crucible or cupola heated by electricity, oil, coal, coke, or gas, and thoroughly mixed therewith. The gray cast iron will then be poured into'molds, resulting in a composition as follows:

Per cent Total carbon 3.00 Combined carbon .70 Silicon 2.00 Manganese 1.00 Sulphur .10 Phosphorus .20 Copper .25 Iron 92.75

The heat of the molten iron will cause the fluorine to evaporate and leave no trace thereof in the final composition of the alloy as cast.

Example II Five pounds of potassium fluoborate having the formula KBF4 will be placed in an iron capsule and added to a molten mass of 1,000 pounds of scrap iron and 1,000 pounds of. pig iron, thoroughly mixed therewith and cast into molds, resulting in the following composition of gray cast iron:

Per cent Total carbon 3.25 Combined carbon .60 Silicon 1.75

Manganese 1.80 Sulphur .10 Phosphorus .50 Iron 92.00

Per cent Total carbon 1.000 to 5.00 Silicon .200 to 3.00 Manganese .200 to 3.00 Sulphur .025 to 0.30 Phosphorus .025 to 1.00

Iron 98.550 to 87.70

In the present specification, whenever the expression gray cast iron is employed, it is intended to signify cast iron containing pearlite and graphitic carbon in such quantities as to make the alloy machinable when cast in any type of mold. Moreover, the expression mixture or charge indicates the contents of the heating container in either a solid or -molt'en state.

The improved machinability of the high strength gray cast iron alloy produced by the present invention is believed to be due to the small graphite particles which are widely separated from each other, and not interlaced.

One advantage of the present invention is that this property of good machinability is attained in a gray cast iron of high tensile and. transverse strength, whereas such good machinability was previously only obtainable with gray cast iron of low tensile strength.

The fluorine catalyst, unlike ferro silicon, apparently has a great afiinity for carbon. This catalyst also has strong deoxidizing properties, decreases or eliminates shrinks, blow holes, and segregation, stabilizes the graphitic and combined carbon, avoids objectionable fumes, and it may be added directly to the molten alloy without loss of its effectiveness.

Unlike slicon carbide it will not increase the percentage of silicon and will not increase the total carbon.

The fluorine catalyst appears to act as a graphite-refining element, and as such decreases the growth of graphite flake.

While in the present invention the catalytic agent has been disclosed as either copper fluoride or potassium fluoborate, by way of example, it will be understood that nickel fluoride, calcium fluoride or potassium fluoride may also be employed within the spirit and scope of the invention. It will also be understood that instead of potassium fluoborate, ammonium fluoborate, sodium fluoborate, calcium fluoborate, barium fluoborate or strontium fluoborate may be employed with almost as good results.

Moreover, in certain applications of our invention, improved results may be obtained by the addition of small amounts of molybdenum, nickel, or copper to the catalyst. In any event, it has been found that the resultant gray cast iron contains from 1.0% to 5.0% total carbon and a combined carbon of .40% to .95%.

In other words, the alloy structure is denser, finer-grained, has pearlite of greater uniformity, and retains the same structure in all cross sections irrespective of the size and cooling rate. The gray iron alloy also restrains chills, and has better properties when heat-treated, including increased tensile and transverse strength.

A further advantage is that the hardness (B. H. N.) in the as-cast condition is not increased, which is probably due to the stabilizing effect of the fluorine on carbide formation. This is evidenced by the minute differences in the hardness between the small and large cross sections produced by varying rates of cooling. Thus, while the as-cast hardness of ordinary cast iron ranges from 180 to 230 Brinell, the as-cast hardness of the improved gray cast iron, herein disclosed, will range from 200 to 250 Brinell, and after oil-quenching will show a Brinell hardness of from 550 to 600. Moreover, a martensitici structure is maintained on tempering or drawing to 1000 degrees Fahrenheit.

Again, the fluorine-treated cast iron will flameharden from 200 ,Brinell as-cast, to 600 Brinell, depending of course on the proportions of carbon, silicon, and manganese. The fluorine treatment herein disclosed also increases the resistance to wear, producing an excellent bearing surface because of the stabilizing effect of the carbide formation.

Moreover, the refining of the graphite structure improves the lubrication property in the iron, which will be less likely to spall on the application of load or heat.

In fact, tests have shown that when the improved fiuoride-treated gray cast iron is repeatedly heated and cooled up to 1600 degrees Fahrenheit, no increase in dimensions will take place. It has also been shown by machinability tests that castings having diflerent cross sections and cooling rates of the fluorine-treated alloy will machine equally well.

While there have been disclosed in this specification two forms in which the invention may be embodied, it is to be understood that these forms are shown for the purpose of illustration only, and that the invention is not to be limited to the specific disclosures, but may be modified and embodied in various other forms without departing from its spirit. In short, the invention includes all the modifications and embodiments coming within the scope of the following claims.

Having thus fully described the invention, what is claimed as new, and for which it is desired to secure Letters Patent, is:

1. The process of making gray cast iron which comprises adding to a charge of molten iron, 25% of copper fluoride, whereby the strength, density, machinability, and wearing qualities of the resultant alloy will be improved.

2. The invention as defined in claim 1, in which the resulting cast iron will have the following composition:

3. The process of making gray cast iron of improved physical and mechanical properties which comprises introducing into a molten mass of iron a small percentage of copper fluoride before the cast iron is poured.

HENRY C. GRIGGS. LAURENCE J. LITALIEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 48,483 Everett June 27, 1865 1,945,260 Davies Jan. 30, 1934 OTHER REFERENCES Cast Metals Handbook, 3rd edition, page 349. Published in 1944 by the American Foundrymens Association, Chicago, Illinois. 

3. THE PROCESS OF MAKING GRAY CAST IRON OF IMPROVED PHYSICAL AND MECHANICAL PROPERTIES WHICH COMPRISES INTRODUCING INTO A MOLTEN MASS OF IRON A SMALL PERCENTAGE OF COPPER FLUORIDE BEFORE THE CAST IRON IS POURED. 